Heat sensitive recording paper

ABSTRACT

IN THE HEAT SENSITIVE RECORDING SYSTEM COMPRISING COMBINATION OF A COLOR FORMING COMPOUND AND A PHENOL COMPOUND, THE FADING OF THE HEAT RECORDING COMPOSITION IN THE DARK CAN BE PREVENTED BY ALLOWING A PHENOL RESIN TO BE PRESENT IN THE HEAT SENSITIVE LAYER OR IN CONTACT WITH THE LAYER. SAID PHENOL RESIN IS THE ONE OBTAINED BY CONDENSATION OF AT LEAST ONE LOWER ALPIPHATIC ALDEHYDES, LOWER ALIPHARIC ALDEHYDE PRODUCING AGENT AND LOWER ALKYLVINYL ESTERS AND A PHENYL COMPOUND HAVING 3 OR MORE ORTHO-AND/OR PARA-POSITIONS (TO PHENOLIC HYDROXYL GROUP) HAVING NO MORE SUBSTITUENTS.

United States Patent "ice 3,829,401 HEAT SENSITIVE RECORDING PAPERKiyoshi Futaki, Kozo Haino, and Isao Kohmura, Kyoto, gapan, assignors toMitsubishi Paper Mills, Ltd., Tokyo,

apan No Drawing. Filed Oct. 25, 1972, Ser. No. 300,873 Claims priority,application Japan, Oct. 30, 1971, 46/ 86,341 Int. Cl. B41n 5/22 U.S. Cl.260-38 8 Claims ABSTRACT OF THE DISCLOSURE In the heat sensitiverecording system comprising combination of a color forming compound anda phenol compound, the fading of the heat recording composition in thedark can be prevented by allowing a phenol resin to be present in theheat sensitive layer or in contact with the layer. Said phenol resin isthe one obtained by condensation of at least one of lower aliphaticaldehydes, lower aliphatic aldehyde producing agent and lower alkylvinylethers and a phenol compound having 3 or more ortho-and/orpara-positions (to phenolic hydroxyl group) having no substituents.

The present invention relates to a heat sensitive recording compositionand a heat sensitive recording paper and more particularly it concernsprevention of fading of heat recording composition of the heat sensitiverecording paper comprising combination of a usually colorless orlight-colored color forming compound and a phenol compound.

It was known that a coating liquid obtained by dispersing in a binder aleuco lactone or spiropyran compound which is a usually colorless orlight-colored color forming compound and a phenol compound which issolid at normal temperature and which is molten or gasified at atemperature of about 60-220 C. in fine particle state is coated on asubstrate to obtain a heat sensitive recording paper. However, suchconventional heat sensitive recording paper is apt to gradually fadewith the lapse of time during storage even in the dark after heatrecording and often causes practically serious defects.

As the results of extensive researches on production of a heat sensitiverecording paper having no defects as mentioned above, the inventors havesucceeded in producing a heat sensitive recording composition which isprevented from fading by the following method. That is, the heatsensitive recording composition of the present invention comprises (1)usually colorless or light-colored color forming compound, (2) a phenolcompound which causes color formation of said compound (1) and (3) athree-dimensionally cross-linked phenol resin, said three componentsbeing dispersed in a binder. That is, the present invention is based onthe discovery that in the heat sensitive system comprising thecombination of a color forming compound and a phenol compound, thefading of the heat recording material in the dark can be markedlyprevented by allowing said phenol resin to be present in a heatsensitive layer or in contact with the layer.

One of the causes of the fading is considered as follows: Lactone orspiropyran compound is stably present as developed color in dissolvedstate or in solid solution state in the molten phenol compoundimmediately after writing with heat. However, with the lapse of time,crystallizations of the phenol compound and the dye constituting thedeveloped color images are gradually accelerated especially by humidityand a suitable temperature to form respectively independent phases,whereby 3,829,401 Patented Aug. 13, 1974 dye molecules are instabilizedto return to the original colorless color forming compound.

The effects of the present heat sensitive recording composition will bedetailedly explained in the Examples.

The normally colorless or light-colored color forming compounds used inthe present invention are known as so-called leuco lactone andspiropyran compounds th representatives of which are as follows:

Crystal violet lactone Malachite Green lactone 3,3-Bis(p-dimethylaminophenyl)-6-amino phthalide3,3-Bis(p-dimethylaminophenyl)-6-p-toluene sulfonamide phthalide3-Diethylamino-7-dibenzylamino fluoran 3 -Diethylamino-7-(N-methylanilino -fluoran 3-Dimethylamino-6-methoxy-fluoran3-Diethylamino-6-methyl-7-chlorofluoran3-Dibutylamino-6-methyl-7-chlorofluoran 3-Diethylamino-7-phenylfluoran3-Morpholino-5,6-benzofiuoran Spiro 1-benzopyran-2,2'-naphthopyran)6-Chloro-8-methoxy-1',3',3-trimethyl-spiro( l-benzopyran-2,2-indoline)The phenol compounds used in the present invention are those which aresolid at normal temperature and are molten and/or gasified at atemperature of about -220 C. to react with said color forming compoundto cause color formation of this compound. Especially, the phenolcompounds which are difficultly soluble in water or petroleum and have amelting point of C. are practically preferred. The examples of thecompounds are as follows:

4,4'-Isopropylidene diphenol 4,4'-Isopropylidene-bis (Z-methylphenol)4,4-Isopropylidene-bis (Z-phenylphenol)4,4'-Isopropylidene-bis(2-tertiary butyl phenol) 4,4-Secondarybutylidene-diphenol 4,4-Secondary butylidene-bis(2-methylphenol)4,4'-Cyclohexylidene-diphenol4,4'-Cyclohexylidene-bis(2-isopropylphenol) 4,4'-Ethylidenediphenol2,2-Methylenebis(S-methylphenol) 4,4'-Ethylidene-bis(Z-methylphenol)4,4-( l-Methylpentylidene -diphenol 4,4'-( l-Methyl-isopentylidene-diphenol 4,4'-( l-Methyl-Hexylidene -diphenol 4,4'- l-Ethyl-butylidene)-diphenol 4,4'-( l-Ethyl-propylidene -bis (Z-methyl phenol)4,4'-Isopropylidene-dicatechol 4,4'-Benzyliclenediphenol4,4-Isopropylidene-bis (2-chlorophenol) 2,2-Dihydroxydiphenyl2,2'-Methylene-bis(4-chlorophenol) 2,2-Methylene-bis(4-methyl-6-tertiarybutylphenol) 4,4'-Isopropylidene-bis(2,6-dimethylphenol)2,2-thiobis(4,6-dimethylphenol) 4,4-Ethylenediphenol 4,4'-(l-Methylbenzylidene)-diphenol is one which has totally 3 or moreortho-positions and/ or para-positions (to phenolic hydroxyl group)having no substituents in one molecule. The representatives thereof maybe represented by the following general formulas,

(wherein R is hydrogen, a hydroxyl group, an alkyl group, an alkoxygroup or a halogen) or R2 a a (11) [wherein R is hydrogen or hydroxylgroup, R is hydrogen, hydroxyl group, a halogen, an alkyl group or analkoxy group and X is S, 0, S phenylene or Phenol,

m-Cresol,

m-Ethoxy phenol,

m-Chlorophenol, 2,4'-Methylene-diphenol, 4,4-Isopropylidenedi-resorcinol, 2,2-Methylene bis 5-bromophenol 4,4-Isopropylidenebis(3-chlorophenol), 2,2-Methylene bis(5-isopropylphenol), 4,4-Ethylenebis 3-methoxyphenyl) 4,4'Isopropylidene-diphenol 4,4'-Secondarybutylidene-diphenol 4,4Cyclohexylidene-diphenol 4,4'-Ethylidene-diphenol4,4-( l-Methylpentylidene) diphenol 4,4-( l-Methyl-isopentylidenediphenol 4,4'-( l-Methyl-hexylidene diphenol 4,4'-( 1-Ethylbutylidene)diphenol 4,4'-Isopropylidene-dicatechol 4,4'-Benzylidene-diphenol4,4,4-Methy1-triphenol 4,4'-( l-Methylbenzylidene) diphenol4,4'-Ethylene diphenol 4,4-Tetramethylene diphenol 4,4'-Hexamethylenediphenol 4,4-Thio diphenol 2,4-Sulphenyl diphenol 2,2'-Oxy diphenol.

The phenol resins may be used in combination of two or more in thepresent invention.

The phenol resins used in the present invention can be easily preparedby reacting said starting phenol com pounds and said lower aliphaticaldehydes or similar cross linking agents in the presence of an acidcatalyst, usually in a solvent, grinding the resultant condensate and,if necessary, washing the ground condensate. Especially, a gelledcondensate of 4,4'-isopropylidene diphenol and formalin is suitable foreconomical reasons. Practically, those which are not softened at lowerthan 130 C. are preferred. Among phenol resins, some of the knownnovolak phenol resins prepared by the reaction of formalin and phenolcompounds having two unsubstituted orthoand/or para-positions tophenolic hydroxyl group in one molecule such as cresol,tert-butylphenol,

octylphenol, phenylphenol, etc. are similarly effective for preventionof fading of heat recording composition. However, being diiferent fromthe phenol resins of the present invention, these known phenol resinsdamage the heat stability of heat sensitive composition when jointlyused in the heat sensitive composition and apt to cause gradual deepcolor formation in the ground of heat sensitive recording layer becausethese known phenol resins have low melting point and cause reduction ofcolor formation temperature due to mixed melting effect with the phenolcompound used as a color forming agent. Thus, these known phenol resinsare not suitable. On the other hand, the phenol resins used in thepresent invention have the property that they are insoluble in solventssuch as methanol, but swollen therein. Fading of a heat sensitive layerin the dark which contains said phenol resins can be prevented by themelting of the phenol compound which is a color forming agent by heatingto cause the phenol resins to swell and the phenol resins have noproperty of decreasing the melting point of the phenol compound to causereduction of color forming temperature. Therefore, these phenol resinshave no such defect as lowering heat stability as seen when other phenolresins are used.

The weight ratio of the phenol compound and phenol resin in the heatsensitive compositions of the present invention is 1:20-20:1 andpreferably 1:5-5 :1. When the amount of thephenol compound is too small,the density of the recorded matter is low and when the amount of thephenol resin is too small, the elfect of prevention of fading is notsatisfactory.

According to the present invention, generally the above mentioned threecomponents are dispersed in water or petroleum and coated on a supportsuch as paper or film. Therefore, a binder for binding said componentsis nec essary. As the binder, generally known water soluble resins aresuitable and examples thereof are polyvinyl alcohol, hydroxyethylcellulose, gum arabic, styrenemaleic acid copolymer, gelatin, etc. Asthe petroleum binder, terpene resins, petroleum resins, cyclized rubber,etc. may be used. In the present invention, as mentioned before, thenormally colorless or light-colored color forming compound, the phenolcompound and the pheol resin are dispersed in a binder and in this case,the dispersed particles are preferably ground to those of as small aspossible, specifically of less than several ,u in diameter. In thiscase, when particle size is large, the surface of coating on a heatsensitive recording paper is naturally roughened and the commercialvalue thereof is reduced. Furthermore, as a grinding assistant, theactivators such as dispersant, defoaming agent, etc. may be used, ifnecessary. Moreover, waxes can be added to a heat sensitive layer tobring about the effect of preventing color formation due to pressure.Additionally, talc, zinc oxide, titanium oxide, calcium carbonate, etc.may also be added to result in white appearance of heat sensitiverecording layer.

SYNTHESIZING EXAMPLE 1 OF THE PHENOL RESIN 4,4'Isopropylidene-diphenol g45.6 Ethyl alcohol -ml 60 Water ml 40 37% Aqueous solution offormaldehyde g 30 Concentrated hydrochloric acid and I water (1:1) ml 10The above components were introduced into a flask and mixed. Then, themixture was refluxed with heat on a water bath for 3 hours. Afterallowing it to stand for cooling, the supernatant liquid was removed bydecantation and the residue was kneaded with water and washed by thedecantation method. Furthermore, 200 ml. of methanol was added theretoand after allowing to stand overnight, the supernatant was removed bydecantation. The residual gel-like material was ground with a householdmixer in the presence of water and then was filtered, washed with waterand dried to obtain slightly browncolored substantially white powders,which were not molten at a temperature of lower than 200 C. Yield was 46g.

SYNTHESIZING EXAMPLE 2 OF THE PHENOL RESIN The procedure of SynthesizingExample 1 was repeated except that 4,4'-(l-methylhexylidene)diphenol wasused in place of 4,4'-isopropylidene-diphenol to obtain substantiallywhite powdery bisphenol resin.

SYNTHESIZING EXAMPLE 3 OF THE PHENOL RESIN The procedure of SynthesizingExample 1 was repeated except that 4,4-cyclohexylidene diphenol was usedin place of 4,4'-isopropylidene-diphenol to obtain substantially whitepowdery bisphenol resin.

Example 1 Liquid A: G. Crystal violet lactone 1 5% aqueous solution ofhydroxyethyl cellulose" 5 Water 5 Liquid B:

4,4 (l Methylhexylidene)-diphenol 4 Resin obtained by condensation of4,4'-isopropylidene diphenol and formalin (Synthesis Example 1) 1 5%Aqueous solution of hydroxyethyl cellulose 25 Water 22 Said liquids Aand B were separately ground and dispersed in a ball mill for 2 days andthey were mixed. The mixture was coated on an ordinary paper having aweight of 50 g./m. in such a manner that the coating amount when driedwas about 4 g./m. and was dried at lower than 40 C. to obtain a heatsensitive recording paper. The ground color of the coating layer waswhite and was stable even when it was stored at room temperature for along period and rapidly formed clear deep blue color by hot pen or hotwriting. Substantially no fading of this paper was caused even when itwas filed and stored for a long period. On the other hand, a recordingpaper which contained no phenol resin of the present invention in theheat sensitive layer gradually faded after heat recording. Moreover, arecording paper which contained a phenol resin from p-octylphenol,p-butylphenol, p-phenylphenol, etc. in place of the phenol resin of thepresent invention did not fade after heat recording, but the graduallyformed ground color and this was not preferred in practical use.

Table 1 shows the results of heat resistant test on these heat sensitiverecording paper.

cording paper was obtained in accordance with the same method as inExample 1. The ground color was white and deep red color was formed byheat recording. Substantially no fading of the heat recording materialin the dark was recognized. On the other hand, fading of portions ofletter written with heat was gradually caused when the bisphenol resinof the present invention was omitted from said heat sensitivecomposition.

Example 3 Liquid A: G. Crystal violet lactone 1 5% Aqueous solution ofpolyvinyl alcohol 5 Water 4 Liquid B:

4,4-Isopropylidene-diphenol 4 Resin obtained by condensation of4,4-isopropylidenediphenol and formalin (Synthesizing Example 1) 5%Aqueous solution of polyvinyl alcohol 25 Water 20 Using the aboveliquids A and B, a heat sensitive recording paper was obtained in thesame manner as in Example 1. The ground color of this paper was whiteand deep blue color was formed by writing with heat. Substantially nofading of the written letters in the dark was recognized. On the otherhand, when the bisphenol resin of the present invention was omitted,fading of the written letters gradually occurred.

Example 4 A heat sensitive recording sheet was obtained in the samemanner as of Example 3 except that a condensation product of4,4'-(l-methylhexylidene)diphenol of Synthesis Example 2 and formalinwas used in place of the phenol condensate of Synthesizing Example 1used in Example 3. The ground color of thus obtained sheet was white andformed deep blue color by writing with heat. These written lettersshowed substantially no fading in the dark.

Example 5 A heat sensitive recording sheet was obtained in the samemanner as of Example 3 except that a condensation product of4,4-cyclohexylidene diphenol of Synthesizing Example 3 and formalin wasused in place of the phenol TABLE l.STABILITY OF HEAT SENSITIVERECORDING PAPER Portions of letter Written with heat Optical density ofground color Fading after After one After one one week at Before week atweek at 40 C.

Phenol resin in heat sensitive layer heating 40 C. 50 0. (percent) None0. 03 0. 04 O. 0 0 Phenol resin of synthesizing, Example 1 (the presentin- 6 9 vention) 0. 04 0. O5 0. 08 0 #51042-0 1 (not the presentinvention) 0.06 0.28 0.32 0

#26799 1 (not the present invention)..- 0. 06 0.10 0.22 0

#26141 3 (not the present invention)..- 0.15 0.26 0.63 0

#51027 4 (not the present invention)... 0. 04 0.09 0. 15 50 1 #51042-0:Para-tert-octyl phenol resin (m.p. 8090 C.) manufactured by SumitomoDurez K. K.

2 #26799: Para-tertbuty1 phenol resin (m.p. 80 O.) manufactured byHooker Chemical Co.

condensate of Synthesizing Example 1 used in Example 3. The resultantsheet had the same properties as in Example 4.

What is claimed is:

1. A fading-prevented, heat sensitive recording composition whichcomprises:

(1) a normally colorless or light-colored color forming compoundselected from the group consisting of leuco lactone and spiropyrancompounds;

(-2) a phenol compound capable of causing color formation of said colorforming compound upon heating; and

(3) a three-dimensionally cross-linked phenol resin which is acondensation reaction product of at least one lower aliphatic aldehyde,lower aliphatic aldehyde producing agent or a lower alkyl vinyl etherand a phenol compound having at least 3 ortho positions or parapositions or ortho and para positions to the phenolic hydroxyl groupfree of substituents, and the weight ratio of said phenol compound (2)to said phenol resin (3) being from 1:20 to 20:1.

2. A heat sensitive recording composition according to claim 1 whereinthe phenol resin is a condensation product of a phenol withformaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acrolein,glyoxal, paraformaldehyde, paraldehyde, methyl vinyl ether, or ethylvinyl ether.

3. A heat sensitive recording composition according to claim 2 whereinthe phenol resin is a condensation product of a phenol and an aldehyde.

4. A heat sensitive recording composition according to claim 3 whereinthe aldehyde is formaldehyde.

5. A heat sensitive recording composition according to claim 2 whereinthe phenol of the phenol resin has the formula HO X- OH I R: a s 2 Tat.

where R, and R are hydrogen, alkyl, phenyl, hydroxyphenyl or a cyclicalkylene group to which R and R are bonded and n is an integer from 0 to8.

6. A heat sensitive recording composition according to Claim 1, whereinsaid phenol compound is one which is solid at normal temperature andwhich is liquefied or gasified at a temperature of --220 C. and reactswith said color forming compound to cause color formation of the colorforming compound.

7. A heat sensitive recording paper which comprises a support and theheat sensitive recording composition of Claim 1 which is coated on saidsupport.

8. A heat sensitive recording composition according to Claim '1, whereinsaid phenol resin is a condensation reaction product of4,4'-isopropylidene diphenol and formalin.

References Cited UNITED STATES PATENTS 3,539,375 11/1970 Baum 11736.8 X3,663,256 5/1972 Miller et al. 117-36.2 3,322,557 5/1967 Schwab ll736.8X

ALLA-N LIEBERMA N, Primary Examiner S. M. PERSON, Assistant Examiner US.Cl. X.R. 11736.2, 36.8

